There has been known a battery assembly formed of a plurality of connected storage batteries (e.g., a plurality of lithium-ion secondary battery cells).
Patent Document 1 discloses a battery assembly system in which a plurality of series connected battery units, each having multiple storage batteries connected in series, are connected in parallel.
In an assembled battery which consists of series connected battery units (storage battery units) connected in parallel, there occurs the problem in which current flows from a series battery unit of a higher voltage to a series battery unit of a lower voltage during charging due to voltage variation between series connected battery units. Therefore, it is necessary that voltage variability between series connected battery units be reduced.
In the battery assembly system disclosed in Patent Document 1, a current control device that can control the magnitude of electric current flowing through itself, e.g., MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is connected in series with each of the series connected battery units so as to regulate the current flowing through the series connected battery units by controlling all the current control devices at the same time, whereby the voltage variation between the series connected battery units is reduced.